Judomaster's secret identity was Hadley "Rip" Jagger, a sergeant in World War II in the U.S. Army. He rescued the daughter of a Pacific island chief and in return was taught the martial art of judo.
After Charlton comics ceased publication, the rights to Judomaster were sold to DC Comics. In post-Crisis continuity, Judomaster was said to be a member of the All-Star Squadron, DC's team of superheroes during World War II, although he has never appeared in an actual published story as a member.